The present invention is generally directed to microcapsule toner compositions, and specifically, to improved microcapsule toner compositions formed by polymerization reactions.
A microcapsule toner is comprised of toner particles in which a core component containing the polymer binder and colorant materials of the toner is surrounded by a shell component. The shell performs a protective function whereby the core material is kept intact until it is required during a reprographic fusing process. The microcapsule toner compositions of the present invention are useful with a variety of known imaging processes including electrophotographic and ionographic imaging processes. In one embodiment, the microcapsule toner compositions can be selected for pressure fixing processes wherein the image is fixed with pressure. Pressure fixing is common in ionographic processes in which latent images are generated on a dielectric receiver such as silicon carbide. The latent images can then be toned with a conductive microcapsule toner by inductive single component development, and transferred and fixed simultaneously (i.e., transfixed) in a single step onto paper with pressure. In another embodiment, the toner compositions of the present invention can be utilized in imaging apparatuses wherein image toning and transfer are accomplished electrostatically, and transferred images are fixed in a separate step by means of a heat fuser or a pressure roll with or without the assistance of thermal or photochemical energy.
In U.S. Pat. No. 3,974,078 to Crystal et al., a toner is disclosed in which at least a major portion of the resin component is a soft polymer encapsulated and dispersed into a tough, polymer matrix in a plurality of discrete domains, instead of a single core.
In U.S. Pat. No. 3,876,610 to Timmerman et al., an electrostatic toner material is disclosed which is composed of particles having a nucleus made of a polymer of an unsaturated monomer surrounded by an outer envelope made mainly of a graft-copolymer of this polymer with an unsaturated monomer grafted with a non-ionic polymer.
In U.S. Pat. No. 4,636,451 to Matkin, pressure-fixable toner-material is disclosed wherein the toner particles comprise a thin, substantially continuous surface layer of polyurea, and an interior portion comprising a matrix of polyurea, the matrix having a colorant and pressure fixable material contained therein. The toner particles contain discontinuities formed by the polyurea matrix which facilitates particle disintegration upon application of pressure to allow low pressure fixability.
Microcapsule toner can be prepared by various physical and mechanical processes. The chemical processes often involve polymerization reactions, including interfacial polycondensation reactions and free radical polymerization. Interfacial polymerization is preferred for forming a microcapsule shell.
Present methods of forming toner using such polymerization reactions produce shells which may be too porous, thus permitting the core material to escape prematurely. A porous shell can be the source of many problems related to inferior operation of the reprographic system, such as core binder diffusion, toner agglomeration, blocking (agglomeration at high temperatures, such as 55.degree. C. over 48 hours), image offset, and decreased shelf life of the toner. If the core binder diffuses out of the shell, it will cause the toner to agglomerate. This results in the problems of poor toner flow and image offset in images processed in the reprographic system.
A porous shell is also prone to breaking, and lacks the necessary mechanical properties to ensure shell integrity. It is desirable to provide a toner with decreased porosity and increased shell integrity.